Add VADTurnAnalyzerUserTurnStopStrategy for speech-to-speech pipelines

For speech-to-speech models like Gemini Live, audio goes directly to the
LLM and transcriptions arrive too late to be useful for turn decisions.
The existing TurnAnalyzerUserTurnStopStrategy waits for STT transcripts
before triggering end-of-turn, adding unnecessary latency.

This adds VADTurnAnalyzerUserTurnStopStrategy which triggers immediately
on turn analyzer COMPLETE without waiting for any STT transcript. Also
fixes the Gemini Live local VAD example to use UserStartedSpeakingFrame/
UserStoppedSpeakingFrame instead of VAD variants, since with local turn
management these are the frames that flow through the pipeline.

examples/realtime/realtime-gemini-live-local-vad.py

@@ -10,6 +10,7 @@ import os
 from dotenv import load_dotenv
 from loguru import logger
 
+from pipecat.audio.turn.smart_turn.local_smart_turn_v3 import LocalSmartTurnAnalyzerV3
 from pipecat.audio.vad.silero import SileroVADAnalyzer
 from pipecat.frames.frames import LLMRunFrame
 from pipecat.pipeline.pipeline import Pipeline
@@ -28,6 +29,9 @@ from pipecat.services.google.gemini_live.llm import GeminiLiveLLMService, Gemini
 from pipecat.transports.base_transport import BaseTransport, TransportParams
 from pipecat.transports.daily.transport import DailyParams
 from pipecat.transports.websocket.fastapi import FastAPIWebsocketParams
+from pipecat.turns.user_start import VADUserTurnStartStrategy
+from pipecat.turns.user_stop import VADTurnAnalyzerUserTurnStopStrategy
+from pipecat.turns.user_turn_strategies import UserTurnStrategies
 
 load_dotenv(override=True)
 
@@ -73,6 +77,12 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
     user_aggregator, assistant_aggregator = LLMContextAggregatorPair(
         context,
         user_params=LLMUserAggregatorParams(
+            user_turn_strategies=UserTurnStrategies(
+                start=[VADUserTurnStartStrategy()],
+                stop=[
+                    VADTurnAnalyzerUserTurnStopStrategy(turn_analyzer=LocalSmartTurnAnalyzerV3())
+                ],
+            ),
             vad_analyzer=SileroVADAnalyzer(),
         ),
     )